Phase Behavior of H[subscript 2] + H[subscript 2]O at High Pressures and Low Temperatures
- CIW
Whereas several clathrate-like structures are known to exist from mixtures of H{sub 2} + H{sub 2}O under pressure, the combined high-pressure and low-temperature region of the phase diagram remains largely unexplored. Here we report a combined Raman spectroscopy and synchrotron X-ray diffraction study on the low-temperature region of the phase diagram. Below 120 K, the H{sub 2} vibron originating from the clathrate 2 (C{sub 2}) phase splits into two distinct components, yet X-ray diffraction measurements reveal no structural change between room temperature and 11 K. We suggest that the two vibrons of the C{sub 2} phase at low temperature originate from vibrational transitions of hydrogen molecules in the ground and first excited rotational energy levels. At 1 GPa we observe the clathrate 1 (C{sub 1}) phase to persist to the lowest temperature measured (80 K). Upon decompression from the C{sub 2} phase we observed the appearance of cubic ice (I{sub c}), which converted to a new phase before transforming to the C{sub 1} phase. The structure of the new phase is consistent with a water framework similar to {alpha}-quartz; the structure could also be related to the tetragonal clathrate phase reported previously for nitrogen and argon guests.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- NSFDOE - BASIC ENERGY SCIENCESNNSA
- OSTI ID:
- 1021793
- Journal Information:
- J. Phys. Chem. C, Vol. 115, Issue (11) ; 03, 2011; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- ENGLISH
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